A typical pallet-type bulk container as described in U.S. Pat. Nos. 5,958,747 5,058,747 and 5,253,776 comprises a large flexible bladder, typically made of plastic and capable of holding a volume of about one cubic meter that sits on a pallet and is surrounded by a metallic cage. The bladder is normally filled with a liquid or a fluent powder so that the full container can easily weigh around 1 ton.
Such a valve typically comprises a housing defining a flow passage, a valve body movable in the passage between a closed position blocking flow through it and an open position permitting free flow, and an actuating element or handle for moving the valve body between its positions. The housing is normally made of plastic, e.g. polyethylene (PE), with an upstream or intake side formed as a nipple connected fixedly to the bladder of the container and a downstream or output side also formed as a nipple that can be threaded to allow connection of a hose. A tear-out disk can be integrally formed in the output side as a tamper indicator and to provide an extra protection against leakage. The valve body is typically of the quarter-turn type, constituted as a disk that extends perpendicular to the axis of the flow passage in the closed position and parallel to it in the open position. Such a valve is described in EP 1,547,967 of H. Bour.
When such a valve is used for the transport and storage of combustible, flammable, or explosive media, for example liquids or bulk materials, electrostatic charges must be avoided for safety reasons. This requires grounding the container's contents. Since the goods are completely surrounded by the normally dielectric bladder, the standard way of doing this is by means of the drain valve that is always at the lower region of the container and thus in continuous contact with its contents. For this reason it has been proposed for the valve housing of a drain valve of the above-described type to be made completely of an electrically conductive plastic. Such electrically conductive plastics are known in principle, and may be, for example, polyethylene to which electrically conductive particles are added. The problem that this causes is that such plastics are not strong and rigid enough. The valve housing can deform, making the valve impossible to operate, or causing a leak.